Contra-rotating fan arrangement and fan drive system for evaporative cooling equipment

ABSTRACT

A counter-rotating fan system for evaporative cooling equipment. The system can include a first axial fan disposed in an air conduit of an evaporative equipment unit, a second axial fan disposed in the air conduit and arranged coaxially with the first fan, a transmission for driving the first axial fan and the second axial fan, and a motor for driving the transmission, wherein the direction of rotation of the first axial fan is opposite to the direction of rotation of the second axial fan.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 13/678,095, filed Nov. 15, 2012 and entitled Contra-Rotating Fan Arrangement And Fan Drive System For Evaporative Cooling Equipment, the entire contents of which are hereby incorporated by reference.

BACKGROUND

Common applications for evaporative cooling equipment such as cooling towers include providing cooled process fluid for HVAC, manufacturing, refrigeration and electric power generation. The cooling towers serve to transfer heat from the process fluid into the surrounding environment.

In an open circuit cooling tower, the process fluid that needs to be cooled is delivered to the cooling tower and distributed over a heat transfer medium, also known as fill, typically by a series of nozzles that atomize the water over the fill. The fill facilitates heat transfer by promoting evaporation through commingling the process fluid with dry outside air. The fill provides a large surface area and provides a required time of contact between the process fluid and the dry, unsaturated airstream supplied by the fan within the cooling tower. As the process fluid droplets pass through the fill, heat is transferred to the atmosphere through the saturated discharge airstream of the cooling tower. A portion of the process fluid is lost through the endothermic process of evaporation leaving the remaining process fluid at a lower temperature than before it entered the cooling tower. The cooled water is collected in a collection basin at the bottom of the cooling tower and then withdrawn therefrom.

Closed circuit cooling towers, also known as fluid coolers, have similar functionality, with the difference being that the process fluid is contained within a serpentine coil and not directly exposed to the surrounding environment. Water stored in the basin of the unit is sprayed over the coils to promote heat transfer from the liquid to the make-up water, while at the same time promoting the endothermic process of evaporation. The end result is the process fluid within the coil is cooled through evaporation of spray water on the outside surface of the coil and to a much lesser degree some heat is transferred through the temperature gradient between the spray water and the coil when atmospheric conditions allow. Evaporative condensers are substantially identical to a closed circuit cooling tower or fluid cooler, except for the process medium. In an evaporative condenser, a refrigerant is used as the process medium, in lieu of process fluids. The evaporative condensers are typically used in the refrigeration industry comprising of cold storage, ice skating rinks, cryogenics, and so forth.

Airflow through evaporative cooling equipment is typically facilitated by a fan in combination with an intake air conduit and an exhaust air conduit, which are provided for each heat transfer section, or cell, of the cooling tower. In induced draft equipment, the fan is mounted near the exhaust of the evaporative cooling unit and draws air from the intake through the interior of the cooling unit and across the fill and drift eliminator sections. In forced draft equipment, the fan is mounted near the intake and pushes the air through the interior of the cooling unit, across the fill and drift eliminators, and out via the exhaust. Typically, the evaporative cooling equipment systems that use axial fans for these applications are single-stage systems.

Several considerations are present in the installation and design of evaporative cooling systems, including airflow, sound output, space requirements, energy requirements, and vibration transmission. It is desirable to minimize noise emitted by operation of the fan, the energy consumed by the fan drive system, and the vibrations emitted by the fan drive system. However, minimizing these negative attributes requires reducing the rotational speed of the fans, which reduces airflow and static pressure below the required minimums to maintain the endothermic process of evaporation within a given evaporative cooling unit. A solution to minimize the negative attributes of cooling tower operation while meeting minimum airflow and static pressure requirements of a given evaporative cooling unit is therefore desired.

SUMMARY

According to at least one exemplary embodiment, a counter-rotating fan system for evaporative cooling equipment is disclosed. The system can include a first axial fan disposed in an air conduit of an evaporative equipment unit, a second axial fan disposed in the air conduit and arranged coaxially with the first fan, a transmission for driving the first axial fan and the second axial fan, and a motor for driving the transmission, wherein the direction of rotation of the first axial fan is opposite to the direction of rotation of the second axial fan.

According to another exemplary embodiment, an evaporative cooling equipment unit is disclosed. The unit can include an enclosure, at least one air conduit, a first axial fan disposed in the at least one air conduit, and a second axial fan disposed in the at least one air conduit and arranged coaxially with the first fan, wherein the direction of rotation of the first axial fan is opposite to the direction of rotation of the second axial fan, and wherein the speed of rotation of the first axial fan is different than the speed of rotation of the second axial fan.

BRIEF DESCRIPTION OF THE FIGURES

Advantages of embodiments of the present invention will be apparent from the following detailed description of the exemplary embodiments. The following detailed description should be considered in conjunction with the accompanying figures in which:

FIG. 1 a shows a first exemplary embodiment of a counter-rotating fan system for evaporative cooling equipment.

FIG. 1 b shows an exemplary embodiment of a transmission for a counter-rotating fan system.

FIG. 2 a shows a second exemplary embodiment of a counter-rotating fan system for evaporative cooling equipment.

FIG. 2 b shows an exemplary embodiment of a transmission and fan hub for a counter-rotating fan system.

FIG. 3 shows a third exemplary embodiment of a counter-rotating fan system for evaporative cooling equipment.

FIG. 4 shows a fourth exemplary embodiment of a counter-rotating fan system for evaporative cooling equipment.

FIG. 5 shows a fifth exemplary embodiment of a counter-rotating fan system for evaporative cooling equipment.

FIG. 6 a shows a sixth exemplary embodiment of a counter-rotating fan system for evaporative cooling equipment.

FIG. 6 b shows an exemplary embodiment of a transmission for a counter-rotating fan system.

DETAILED DESCRIPTION

Aspects of the invention are disclosed in the following description and related drawings directed to specific embodiments of the invention. Alternate embodiments may be devised without departing from the spirit or the scope of the invention. Additionally, well-known elements of exemplary embodiments of the invention will not be described in detail or will be omitted so as not to obscure the relevant details of the invention. Further, to facilitate an understanding of the description discussion of several terms used herein follows.

As used herein, the word “exemplary” means “serving as an example, instance or illustration.” The embodiments described herein are not limiting, but rather are exemplary only. It should be understood that the described embodiment are not necessarily to be construed as preferred or advantageous over other embodiments. Moreover, the terms “embodiments of the invention”, “embodiments” or “invention” do not require that all embodiments of the invention include the discussed feature, advantage or mode of operation.

According to at least one exemplary embodiment, counter-rotating fan systems for evaporative cooling equipment may be disclosed. The fan systems may include a pair of coaxial, counter-rotating fans and associated drive and transmission components.

FIG. 1 a shows a first exemplary embodiment of a counter-rotating fan drive system 100 for evaporative cooling equipment. System 100 can include a first fan 102 and a second fan 104, which may be disposed in an air conduit 106. Air conduit 106 may be in fluid communication with the interior of evaporative cooling unit 10 and the exterior environment. The fans 102, 104 and air conduit 106 may be provided in any location on an evaporative cooling equipment unit 10 that enables system 100 to function as described herein. In some exemplary embodiments, air conduit 106 may be an exhaust air conduit, for example in an induced draft cooling unit. In other exemplary embodiments, air conduit 106 may be an intake air conduit, for example in a forced draft cooling unit. Air conduit 106 may also function as a fan cowl for fans 102, 104.

The first fan 102 and second fan 104 may be axial fans and may be arranged coaxially with respect to each other. In some exemplary embodiments, fans 102, 104 may include removable airfoil-type blades which may be pitched to a desired angle. The blades may be pitched such that the blade pitch of first fan 102 may be different from the blade pitch of second fan 104.

A motor 108 may be provided to drive system 100. Motor 108 may be an electric motor, or any motor known to one having ordinary skill in the art that enables system 100 to function as described herein, and may have any power rating suitable for the particular application of system 100. Motor 108 may drive an output shaft 110 on which a drive pulley 112 is mounted. Drive pulley 112 may engage a belt 114, which can in turn engage a driven pulley 116 that is coupled to an input shaft 118 of transmission 120.

Transmission 120 may drive fans 102, 104 via first and second output shafts 122, 124. First fan 102 may be rigidly coupled to first output shaft 122, while second fan 104 may be rigidly coupled to second output shaft 124. Output shafts 122, 124 may be arranged coaxially with respect to each other such that first output shaft 122 drives first fan 102 and second output shaft 124 drives second fan 104. To that end, second output shaft 124 and second fan 104 may each have a bore defined therein, the bores being sized such that first shaft 122 may pass through the bore. Transmission 120 may include gearing arrangements for rotating the output shafts 122, 124 at speeds different from the speed of the input shaft 118.

Transmission 120 may also include gearing arrangements, for example a planetary gearset, that are adapted to drive first fan 102 in a direction counter to that of second fan 104. Furthermore, transmission 120 may be adapted to drive first fan 102 at a different speed than second fan 104.

An exemplary embodiment of transmission 120 is shown in FIG. 1 b. In some exemplary embodiments of transmission 120, input shaft 118 may engage first output shaft 122 via a gear or belt drive that may be adapted for gearing reduction. Alternatively, input shaft 118 may be rigidly coupled to, or may function as, first output shaft 122, with gearing reduction provided by pulleys 112, 116. The first output shaft 122 can carry a sun gear 126 a that engages a plurality of planet gears 126 b, which, in turn, engage a ring gear 126 c. The planet gears 126 b are coupled to a carrier 128 that can maintain the positions of the planet gears. Carrier 128 may be held stationary so as to allow the planet gears to act as idlers. The ring gear 126 c may be coupled to second output shaft 124. Thus, in operation, first output shaft can rotate sun gear 126 a, causing ring gear 126 c to rotate in a direction opposite to the sun gear, thereby rotating second output shaft 124 in a direction opposite to that of first output shaft 122. The ratios of the gears may further be adapted to rotate second output shaft 124 at a speed different than that of first output shaft 122.

In yet other exemplary embodiments, transmission 120 may be be substantially similar to that disclosed in U.S. Pat. No. 6,540,570, entitled Counter-Rotating Transmission, the disclosure of which is hereby incorporated by reference in its entirety.

An exemplary layout for counter-rotating fan drive system 100 is shown in FIG. 1 a. A support member 130 may be coupled to an evaporative cooling equipment unit 10. Motor 108 and transmission 120 may be mounted on support member 130. Motor 108 may be mounted in a substantially laterally offset position from transmission 120 and oriented such that belt 114 can engage drive pulley 112 and driven pulley 116. Transmission 120 may be mounted proximate air conduit 106 such output shafts 122, 124 can extend towards fans 102, 104, which may be disposed within air conduit 106. In the exemplary embodiment, support member 130, as well as motor 108 and transmission 120, may be mounted within the interior space of the evaporative cooling unit 10. The specific layout and positioning of the components of system 100 may depend on the configuration of the particular evaporative cooling unit 10 with which system 100 may be used and may be adapted or modified as desired by one having ordinary skill in the art.

FIG. 2 a shows a second exemplary embodiment of a counter-rotating fan drive system 200 for evaporative cooling equipment. For convenience of illustration, substantially similar functional elements to those in the first exemplary embodiment are represented by similar numerals, with the leading digit incremented to 2. Thus, a detailed description of the substantially similar elements may be omitted. The second exemplary embodiment has substantially similar structure and functionality to the first exemplary embodiment, except for the features described below.

In the second exemplary embodiment, motor 208 may drive a drive shaft 210 that may function as, or be coupled to, an output shaft 242 of a transmission 240. Transmission 240 can include any gear arrangement that enables system 200 to function as described herein. The gear arrangement can function to rotate output shaft 242 at a speed different from that of drive shaft 210 of motor 208. For example, the gear arrangement may include an input gear rigidly coupled to drive shaft 210, and an output gear rigidly coupled to output shaft 242 and engaged with the input gear. The input and output gears may have different ratios.

Output shaft 242 of transmission 240 may extend to first fan 202 and may be rigidly coupled thereto so as to drive first fan 202. Second fan 204 may be arranged coaxially with output shaft 242. Second fan 204 may operatively engage output shaft 242 via a fan hub 250. Fan hub 250 can include a bore through which output shaft 242 may extend. Fan hub 250 can further include a stator portion 252 on which second fan 204 may be rotatably mounted. So as to support fan hub 250 and second fan 204 in place, a support structure 256 can extend between, and be coupled to, transmission 240 and the stator portion 252 of fan hub 250.

Fan hub 250 can further include a gear arrangement therein which can be operatively engaged with both output shaft 242 and second fan 204. An exemplary embodiment of fan hub 250 is shown in FIG. 2 b. The gear arrangement can be operable to rotate second fan 204 in a direction opposite to that of output shaft 242 and consequently in a direction opposite to that of first fan 202. The gear arrangement can further be operable to rotate second fan 204 at a speed different from that of output shaft 242 and consequently first fan 202.

In some exemplary embodiments, a sun gear 254 a may be carried by output shaft 242. The sun gear 254 a can engage a plurality of planet gears 254 b, that are disposed within fan hub 250. The planet gears 254 b can, in turn, engage a ring gear 254 c. The planet gears 254 b may be coupled to a carrier 258, which can maintain the positions of the planet gears. Carrier 258 may in turn be coupled to stator portion 252 of fan hub 250, thereby allowing carrier 258 to be held stationary so as to allow the planet gears to act as idlers. The ring gear 254 c may be coupled to, or may be part of, the rotor of second fan 204. Thus, in operation, first output shaft can rotate sun gear 254 a, causing ring gear 254 c to rotate in a direction opposite to the sun gear, thereby rotating second fan 204 in a direction opposite to that of first output shaft 222. The ratios of the gears may further be adapted to rotate second fan 204 at a speed different than that of first output shaft 222.

An exemplary layout for counter-rotating fan drive system 200 is shown in FIG. 2 a. A support member 230 may be coupled to an evaporative cooling equipment unit 20. Motor 208 and transmission 240 may be provided as an integrated unit, and may be mounted on support member 230. Motor 208 and transmission 240 may be mounted proximate air conduit 206 such that output shaft 242 can extend towards fans 202, 204, which may be disposed within air conduit 206. In the exemplary embodiment, support member 230, as well as motor 208 and transmission 220, may be mounted within the interior cavity of the evaporative cooling unit 20. The specific layout and positioning of the components of system 200 may depend on the configuration of the particular evaporative cooling unit 20 with which system 200 may be used and may be adapted or modified as desired by one having ordinary skill in the art.

FIG. 3 shows a third exemplary embodiment of a counter-rotating fan drive system 300 for evaporative cooling equipment. For convenience of illustration, substantially similar functional elements to those in the first exemplary embodiment are represented by similar numerals, with the leading digit incremented to 3. Thus, a detailed description of the substantially similar elements may be omitted. The third exemplary embodiment has substantially similar structure and functionality to the first exemplary embodiment, except for the features described below.

In the third exemplary embodiment, motor 308 may drive a drive shaft 310 that can function as, or be coupled to, an input shaft of transmission 320. Transmission 320 may drive fans 302, 304 via first and second output shafts 322, 324 and may have substantially similar structure and functionality to any of the embodiments of transmission 120.

An exemplary layout for counter-rotating fan drive system 300 is shown in FIG. 3. A first support member 330 and a second support member 332 may be coupled to an evaporative cooling equipment unit 30. Motor 308 may be mounted on support member 330 while transmission 320 may be mounted on support member 332. Motor 308 may be mounted substantially proximate transmission 320. Transmission 320 may be mounted proximate air conduit 306 such output shafts 322, 324 can extend towards fans 302, 304, which may be disposed within air conduit 306. In the exemplary embodiment, support members 330, 332, as well as motor 308 and transmission 320, may be mounted within the interior space of the evaporative cooling unit 30. The specific layout and positioning of the components of system 300 may depend on the configuration of the particular evaporative cooling unit 30 with which system 300 may be used and may be adapted or modified as desired by one having ordinary skill in the art.

FIG. 4 shows a fourth exemplary embodiment of a counter-rotating fan drive system 400 for evaporative cooling equipment. For convenience of illustration, substantially similar functional elements to those in the first exemplary embodiment are represented by similar numerals, with the leading digit incremented to 4. Thus, a detailed description of the substantially similar elements may be omitted. The fourth exemplary embodiment has substantially similar structure and functionality to the first exemplary embodiment, except for the features described below.

In the fourth exemplary embodiment, motor 408 may drive a drive shaft 410, which may be coupled to a connecting shaft 415 via a first coupling 411. Connecting shaft 415 may in turn be coupled to an input shaft 418 of a transmission 420 via a second coupling 411. Couplings 411 may be rigid couplings or may be flexible couplings. A suitable type of coupling may chosen for a particular application by one having ordinary skill in the art.

Transmission 420 may drive fans 402, 404 via first and second output shafts 422, 424 and may have substantially similar structure and functionality to any of the embodiments of transmission 120. The drive shaft 410 and connecting shaft 415 may be oriented at an angle to the output shafts 422, 424 of transmission 420. Therefore, an angle gearing arrangement may be provided. The angle gearing arrangement may be any known gearing arrangement that enables system 400 to function as described herein, and may include gear reduction capabilities. In some exemplary embodiments, the angle gearing arrangement may be disposed external to transmission 420. In other exemplary embodiments, transmission 420 may be adapted by one having ordinary skill in the art to include an angle gearing arrangement therein.

An exemplary layout for counter-rotating fan drive system 400 is shown in FIG. 4. A support member 430 may be coupled to an evaporative cooling equipment unit 40. Motor 408 may be mounted in a substantially laterally offset position from transmission 420 and disposed externally to evaporative cooling unit 40, while transmission 420 may be mounted on support member 430 and disposed within the interior space of unit 40. For example, motor 408 may be mounted on an exterior surface of the enclosure 42 of unit 40. Connecting shaft 415 may extend from motor 408 to transmission 420 via an aperture in the enclosure 42. Transmission 420 may be mounted proximate air conduit 406 such output shafts 422, 424 can extend towards fans 402, 404, which may be disposed within air conduit 406. The specific layout and positioning of the components of system 400 may depend on the configuration of the particular evaporative cooling unit 40 with which system 400 may be used and may be adapted or modified as desired by one having ordinary skill in the art.

FIG. 5 shows a fifth exemplary embodiment of a counter-rotating fan drive system 500 for evaporative cooling equipment. For convenience of illustration, substantially similar functional elements to those in the fourth exemplary embodiment are represented by similar numerals, with the leading digit incremented to 5. Thus, a detailed description of the substantially similar elements may be omitted. The fifth exemplary embodiment has substantially similar structure and functionality to the fourth exemplary embodiment, except for the features described below.

In the fifth exemplary embodiment, motor 508 may drive a drive shaft 510, which may be coupled to an input shaft 518 of a transmission 520 via a coupling 511. Couplings 511 may be a rigid couplings or may be a flexible coupling. A suitable type of coupling may chosen for a particular application by one having ordinary skill in the art.

The drive shaft 510 may be oriented at an angle to the output shafts 522, 524 of transmission 520. Therefore, an angle gearing arrangement may be provided, substantially as described in the exemplary embodiment of system 400.

An exemplary layout for counter-rotating fan drive system 500 is shown in FIG. 5. A support member 530 may be coupled to an evaporative cooling equipment unit 50. Motor 508 may be mounted in a substantially laterally offset position from transmission 520. Transmission 520 may be mounted proximate air conduit 506 such output shafts 522, 524 can extend towards fans 502, 504, which may be disposed within air conduit 506. In the exemplary embodiment, support member 530, as well as motor 508 and transmission 520, may be mounted within the interior space of the evaporative cooling unit 50. The specific layout and positioning of the components of system 500 may depend on the configuration of the particular evaporative cooling unit 50 with which system 500 may be used and may be adapted or modified as desired by one having ordinary skill in the art.

FIG. 6 a shows a sixth exemplary embodiment of a counter-rotating fan drive system 600 for evaporative cooling equipment. For convenience of illustration, substantially similar functional elements to those in the fourth exemplary embodiment are represented by similar numerals, with the leading digit incremented to 6. Thus, a detailed description of the substantially similar elements may be omitted. The sixth exemplary embodiment has substantially similar structure and functionality to the first exemplary embodiment, except for the features described below.

In the sixth exemplary embodiment, motor 608 may drive a drive shaft 610, which may be coupled to a connecting shaft 615 via a first coupling 611. Connecting shaft 615 may in turn be coupled to an input shaft 618 of a transmission 660 via a second coupling 611. Couplings 611 may be rigid couplings or may be flexible couplings. A suitable type of coupling may chosen for a particular application by one having ordinary skill in the art. In other exemplary embodiments, connecting shaft 615 may be omitted, and drive shaft 610 may be coupled to input shaft 618 via a rigid or flexible coupling 611.

Transmission 660 may be disposed in between first fan 602 and second fan 604. A first output shaft 662 may extend to, and be rigidly coupled to first fan 602, and a second output shaft 664 may extend to, and be rigidly coupled to second fan 604. Furthermore, input shaft 618 may be oriented at an angle to the output shafts 662, 664 of transmission 640. Transmission 660 can therefore include a gearing arrangement for transferring power from input shaft 618 to output shafts 662, 664. An exemplary gearing arrangement is shown in FIG. 6 b. For example, the gearing arrangement may include an input gear 666 carried by input shaft 618, a first output gear 668 a carried by first output shaft 662 and engaged with the input gear, and a second output gear 668 b carried by second output shaft 664 and engaged with the input gear. The input and output gears may be bevel gears, and may have differing ratios. Transmission 660 can thus drive output shaft 662 at a different speed than, and in a direction counter to output shaft 664. However, any other configuration for transmission 660 that enables system 600 to function as described herein may be contemplated and provided by one having ordinary skill in the art.

An exemplary layout for counter-rotating fan drive system 600 is shown in FIG. 6 a. A support member 630 may be coupled to an evaporative cooling equipment unit 40 and disposed within the interior space thereof. Fans 602, 604 may be disposed within air conduit 606, and transmission 660 may be mounted within air conduit 606 between fans 602, 604. The fan and transmission assembly may be supported on support member 630 by second shaft 664, which may be coupled to a turntable 634. Turntable 634 may include a fixed portion coupled to support member 630, and a rotating portion to which second shaft 664 may be coupled. The rotating portion may be rotatably coupled to the fixed portion of turntable 634. Bearings, rollers, or any other friction reducing members may be provided to facilitate the rotatable coupling between the rotating portion and the fixed portion of turntable 634.

Motor 608 may be mounted in a substantially laterally offset position from transmission 660 and disposed externally to evaporative cooling unit 60. For example, motor 608 may be mounted on an exterior surface of the enclosure 62 of unit 60. A motor mount 636 may be provided so as to position motor 608 relative to transmission 660 so as to facilitate the coupling between motor 608 and transmission 660. Connecting shaft 615 may extend from motor 608 to transmission 660 via an aperture in the enclosure 62. The specific layout and positioning of the components of system 600 may depend on the configuration of the particular evaporative cooling unit 60 with which system 600 may be used and may be adapted or modified as desired by one having ordinary skill in the art.

The embodiments described herein can provide several advantages over conventional, single-stage fan systems for evaporative cooling equipment. First, due to the increased efficiency inherent to a counter-rotating fan arrangement, lower rotational speeds are required for the fans of the counter-rotating systems disclosed herein. Consequently, utilizing any of the embodiments disclosed herein in a cooling tower can result in decreased noise levels and decreased energy requirements when compared with single-stage fan systems. Furthermore, the embodiments disclosed herein can result in reduced vibration transmission to the evaporative cooling unit, due to the cancelling out of the gyroscopic forces of the fans. The reduced vibration can be beneficial for meeting updated building codes that have strict vibration requirements, and can also facilitate increased life of the mechanical components of the fan drive systems.

Additionally, the dual axial fans of the embodiments disclosed herein can generate higher static pressure within the evaporative cooling unit than can be generated by conventional single stage fan units, which can present several advantages. The higher static pressure can result in an increased thermal performance of the evaporative cooling unit with which the counter-rotating fan system is used. As a result of this higher static pressure, air may be drawn from portions of the cooling unit that are typically known as low-performance areas, such as the corners of the unit or other areas with suboptimal airflow when single stage fans are used. Additionally, the higher static pressure can shrink the air envelope requirement for a cooling unit, thereby facilitating improved flexibility for the layout of the cooling equipment. Furthermore, as a consequence of the increased static pressure, sound attenuation devices may be used in conjunction with the embodiments disclosed herein, as the pressure drops created by the sound attenuation devices are mitigated by the increased pressure generated by the dual axial fans, allowing the evaporative cooling unit to maintain satisfactory thermal performance. Additional advantages of the embodiments disclosed herein include the reduction of the necessity to de-ice the fan blades, as the counter-rotating action of the two axial fans inhibits ice from forming during operation.

The foregoing description and accompanying figures illustrate the principles, preferred embodiments and modes of operation of the invention. However, the invention should not be construed as being limited to the particular embodiments discussed above. Additional variations of the embodiments discussed above will be appreciated by those skilled in the art.

Therefore, the above-described embodiments should be regarded as illustrative rather than restrictive. Accordingly, it should be appreciated that variations to those embodiments can be made by those skilled in the art without departing from the scope of the invention as defined by the following claims. 

1. A counter-rotating fan system for evaporative cooling equipment, comprising: a first axial fan disposed in an air-restricted conduit of an evaporative equipment unit; a second axial fan disposed in the air-restricted conduit and arranged coaxially with the first fan, walls of the conduit closely enclosing the tips of the first axial fan and the second axial fan; a transmission for driving the first axial fan and the second axial fan; and a motor for driving the transmission, the motor and transmission driving the first axial fan and the second axial fan at at least one speed configured to (i) maintain airflow at a minimum value necessary to maintain an endothermic process of evaporation, and (ii) maintain static pressure at a minimum value necessary to maintain the endothermic process of evaporation; wherein the direction of rotation of the first axial fan is opposite to the direction of rotation of the second axial fan.
 2. The fan system of claim 1, wherein the speed of rotation of the first axial fan is different from the speed of rotation of the second axial fan.
 3. The fan system of claim 1, further comprising: a first output shaft coupled to the first axial fan and driven by the transmission in a first direction; and a second output shaft coupled to the second axial fan and driven by the transmission in a direction opposite to the first direction.
 4. The fan system of claim 3, wherein the first output shaft is rotatably disposed within the second output shaft.
 5. (canceled)
 6. The fan system of claim 1, further comprising: a first output shaft coupled to the first axial fan and driven by the transmission in a first direction; and a hub operatively coupled to the first output shaft and the second axial fan, the hub adapted to drive the second axial fan in a direction opposite to the first direction.
 7. The fan system of claim 1, wherein an output shaft of the motor is coupled to an input shaft of the transmission via a belt drive.
 8. The fan system of claim 1, wherein an output shaft of the motor is directly coupled to an input shaft of the transmission.
 9. The fan system of claim 1, wherein an output shaft of the motor is coupled to an input shaft of the transmission via an angle gearing arrangement.
 10. The fan system of claim 1, wherein the air conduit is an air discharge conduit.
 11. The fan system of claim 1, wherein the air conduit is an air intake conduit.
 12. An evaporative cooling equipment unit, comprising: an enclosure; at least one air conduit; a first axial fan disposed in the at least one air conduit; and a second axial fan disposed in the at least one air conduit and arranged coaxially with the first fan; wherein the direction of rotation of the first axial fan is opposite to the direction of rotation of the second axial fan; and wherein the speed of rotation of the first axial fan is different than the speed of rotation of the second axial fan.
 13. The evaporative cooling equipment unit of claim 12, wherein the at least one air conduit is an air discharge conduit.
 14. The evaporative cooling equipment unit of claim 12, wherein the at least one air conduit is an air intake conduit.
 15. The evaporative cooling equipment unit of claim 12, further comprising: a transmission for driving the first axial fan and the second axial fan; and a motor for driving the transmission.
 16. The fan system of claim 1, further comprising: a first output shaft coupled to the first axial fan and driven by the transmission in a first direction; and a second output shaft coupled to the second axial fan and driven by the transmission in a direction opposite to the first direction.
 17. The fan system of claim 16, wherein the first output shaft is rotatably disposed within the second output shaft.
 18. The fan system of claim 1, wherein the transmission is disposed between the first axial fan and the second axial fan.
 19. The fan system of claim 15, further comprising: a first output shaft coupled to the first axial fan and driven by the transmission in a first direction; and a hub operatively coupled to the first output shaft and the second axial fan, the hub adapted to drive the second axial fan in a direction opposite to the first direction.
 20. The fan system of claim 1, wherein the conduit has an internal width, and wherein at least the first axial fan has a blade width which is no less than about ninety percent of the conduit internal width.
 21. An evaporative cooling equipment counter-rotating fan system, comprising: an air-restricted conduit coupled to the evaporative cooling equipment; a first axial fan an a second axial fan disposed inside the air-restricted conduit and arranged coaxially with respect to each other, walls of the conduit closely enclosing the tips of the first axial fan and the second axial fan; a transmission for driving the first axial fan and the second axial fan; and means for driving the transmission to (i) maintain airflow at the minimum value necessary to maintain an endothermic process of evaporation, and (ii)) maintain static pressure at the minimum value necessary to maintain the endothermic process of evaporation, the means for driving rotating of the first axial fan in a direction opposite to the direction of rotation of the second axial fan. 